A so-called sublimation type heat-sensitive transfer recording system comprises heating a transfer recording sheet having provided on one side thereof a coloring material layer formed by coating an ink containing a subliming dye and a binder, by a heating means, e.g., thermal head, and transferring the dye onto a recording sheet by sublimation. Binders which have conventionally been used for forming a coloring material layer are high-molecular compounds having a boiling point or softening point of 100.degree. C. or higher. Particularly suitable binders include acrylic resins, methacrylic resins, polyvinylchloride, polyvinylidenechloride, polystyrene, polyvinylacetal, polyamide, polyvinyl alcohol, polycarbonate, polysulfone, polyethersulfone, cellulose resins, and the like as described in Japanese Patent Application (OPI) No. 14994/84 (the term "OPI" herein used means "unexamined published application").
With the recent tendency toward rapid recording, there has been a demand for heating the transfer recording sheet at higher temperatures. In order to meet this requirement, binders to be used in the transfer recording sheet have been demanded to have further improved heat resistance.
However, since the above-described resins, such as acrylic resins, methacrylic resins, polyvinyl chloride, polyvinylidenechloride polystyrene, etc. are softened or melted to cause adhesion to a recording sheet because of the lack of heat resistance, it has been difficult to obtain satisfactory recording.
Further, binders to be used in the transfer recording sheet should be dissolved in solvents or water in preparation of an ink. However, resins, such as polyamide, polycarbonate, polysulfone, polyethersulfone, etc. have low solubility so that the employable solvents are limited to halogen type solvents, which require much care in handling for safety and hygiene considerations.
In addition, binders to be used in the transfer recording sheet are generally required to have satisfactory compatibility with subliming dyes used. If the binder has poor compatibility with the dye, the dye dissolved in an ink and coated on a base film is crystallized during drying. Such being the case, the dye in non-recorded areas is also transferred to non-recorded areas in contact with a recording sheet to cause background stains, resulting in reduction of recording quality. On this account, polyvinyl alcohol, cellulose resins, etc. do not exhibit satisfactory compatibility with nonionic dyes which are commonly employed as subliming dyes and are, therefore, unfavorable as binders for transfer recording sheets.